Survey of five food-borne pathogens in commercial cold food dishes and their detection by multiplex PCR

Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157, Salmonella spp. and Bacillus cereus are major food-borne pathogens that often contaminate food and cause outbreaks of illness. This investigation determined the incidence of the five pathogens in commercial cold dishes food. A total of 99 samples, consisting of meat, vegetable and soy products were collected and analyzed using conventional culture methods to isolate the bacteria. The results showed that S. aureus, L. monocytogenes and Salmonella spp. were present in cold dishes with their positive rates reaching 8.08%, 6.06% and 2.02%, respectively. All the samples were negative for E. coli O157 and B. cereus. Based on the survey, a triplex PCR was established that uses target genes xcd, vicK and LMOf 2365–2721 for the simultaneous detection of Salmonella spp., S. aureus, and L. monocytogenes, respectively. The detection limit of the multiplex PCR for simultaneously identifying the three target pathogens was 103 cfu/ml. The detection sensitivity of the single PCR for pure DNA of L. monocytogenes, S. aureus and Salmonella spp. was 10.4, 173.7 and 340.3 fg/ul, respectively. The practical sample testing suggests that the detection rate of the three pathogens by multiplex PCR and the conventional culture method was essentially the same. Our results show that multiplex PCR is a rapid, accurate, sensitive and stable method for preliminary screening of these three food-borne pathogens in cold dishes.